Physics News Update 442

>Date: Mon, 9 Aug 1999 14:39:18 -0400 (EDT)>From: AIP listserver <physnews@aip.org>>To: physnews-mailing@aip.org>Subject: update.442>>PHYSICS NEWS UPDATE >The American Institute of Physics Bulletin of Physics News>Number 442 August 9, 1999 by Phillip F. Schewe and Ben Stein>>GRAVITY WAVE ANALYSIS FROM LIGO PROTOTYPE. The>Laser Interferometer Gravitational-wave Observatory (LIGO),>when fully deployed, will consist of two facilities (Hanford, WA>and Livingston, LA). At each site laser beams pass up and down>two perpendicular 4-km-long vacuum pipes, reflecting repeatedly>from mirrors hung from wires. The presence of a passing>gravitational wave would announce itself by a flexing of space->time which would very slightly lengthen the path of light in one>arm and shorten the path in the other arm, causing a subtle change>in the interference pattern made by the converging light beams>from the two arms. The full LIGO, by about November 2001,>should be able to detect a strain, defined as the fractional change in>the position of the mirrors divided by the length of the arm (4 km),>of 10^-21. This is the expected disturbance one expects from the>gravity waves emitted by the coalescence of two solar-sized stars at>a distance from Earth of 30-50 million light years. But before>LIGO scientists possess their full instrument, they do have a 40-m>prototype at Caltech, built for doing engineering studies but also>capable of sensing gravity waves, albeit with the lesser strain>sensitivity of a few times 10^-19. Thus the LIGO team, while>testing methods for searching (directly via gravity waves) for>binary coalescences, have thereby rendered an upper limit for such>events of less than one every two hours in our galaxy. This result>is useful for the test of the procedures, but is not significant for>astronomers, who have previously established more stringent upper>bounds with electromagnetic waves (visible and radio). (Contact >Barry Barish at Caltech, 626-395-3853 or 818-601-2643; Stan>Whitcomb 626-395-2131; or Bruce Allen, University of>Wisconsin-Milwaukee, 626-893-2003 or 414-229-6439; Allen et>al., Physical Review Letters, 16 August 1999.)>>AT THE INTERNATIONAL PHYSICS OLYMPIAD, held in>July, the US team had its second-best showing since it started>competing in 1986, with 3 gold medals and 2 silver medals brought>home by the 5 high school students who participated. In informal>rankings, the US placed 3rd out of the 62 countries that competed,>after Russia and Iran. Taking place this year in Padua, Italy, where>Galileo discovered the 4 Jupiter moons named after him, the>Olympiad contains two days of grueling theoretical and>experimental problems amounting to what is the world's most>difficult high-school physics test. For example, the students had>to compute the precise trajectory of a space probe that uses>Jupiter's gravity as a slingshot--a technique used in real-life>spacecraft such as Cassini. Gold medalists included Peter Onyisi>(Arlington, VA), who had the tenth highest overall score out of the>approximately 300 competitors at the Olympiad, Benjamin>Mathews (Dallas, TX), and Andrew Lin (Wallingford, CT). Silver>medalists include Jason Oh (Baltimore, MD) and Natalia Toro>(Boulder, CO), who earlier this year also became the youngest>person (at 14 years of age) ever to win the top prize of the Intel>(formerly Westinghouse) Science Talent Search. (More>information at http://www.aip.org/releases/1999/release05.html)>>IN-PLANE-GATE (IPG) TRANSISTORS can be excavated using>nanomachining techniques. IPG transistors, in which the source,>drain, and gate all lie in a plane rather than in a sandwich, might be>especially useful for high-frequency applications. Scientists at the>University of Hannover (Hans Werner Schumacher, 011-49-511->762-2523, schumach@nano.uni-hannover.de) have carved out an>IPG structure in a semiconductor surface using the probe from an>atomic force microscope (see figure at >www.aip.org/physnews/graphics). The probe makes an incision>into the material extending down about halfway toward a buried>interface where, lodged between GaAs and AlGaAs layers, a>reservoir of electrons is confined to a plane. The incisions from>above do not penetrate into this two-dimensional electron gas>(2DEG) but they do shape (and can even pinch off) the conduction>of the electrons. The Hannover researchers have also used their>inscribing approach to make single-electron transistors (SETs),>devices that register the coming and going of single electrons. >(Schumacher et al., Applied Physics Letters, 23 August 1999.)>